RhymeZone: niello definitions

Definitions of niello:

noun: (metallurgy) Any of various black metal alloys, made of sulphur with copper, silver or lead, used to create decorative designs on other metals.
noun: An impression on paper taken from the engraved or incised surface before the niello alloy has been inlaid.
verb: (transitive) To decorate (a surface) using this technique.

(Definitions from Wiktionary)